There are many classes of devices. One such class are MEMS (“micro electromechanical systems”) devices. MEMS devices are a class of systems that are physically small. These systems have both electrical and mechanical components. MEMS originally used modified integrated circuit (computer chip) fabrication techniques and materials to create these very small mechanical devices. Today there are many more fabrication techniques and materials available. One such fabrication technique includes sacrificial polysilicon surface micromachining which is a technology that enables the mass production of complex MEMS by themselves or MEMS integrated with microelectronic systems. This technology has already been successfully commercialized as acceleration sensors for automobile airbag deployment.
There are many wide ranging application for MEMS devices. Two main categories of MEMS devices are sensors and actuators. Micro sensors are useful because their small physical size allows them to be much less invasive. Micro actuators are useful because the amount of work they perform is very precise. A polysilicon resonator transducer is an example of a MEMS sensor which uses stress controlled thin film polysilicon process to form a mechanically free beam of polysilicon having resonant frequency can be measured electronically. Environmental changes can be converted to a changes in resonant frequency of the micro beam. The environmental changes can be sensed.
Other MEMS devices include magnetic micro motors fabricated by a deep x-ray lithography and electrode position process. The rotor is magnetically salient to allow a magnetic field applied to each of the two poles to cause the rotor to turn. External loading gears can be added. Gears are fabricated that are 100 microns tall. Techniques for forming MEMS devices can be used to create parts of systems where high tolerances are necessary which can bridge the gap between MEMS and traditionally machined precise components. MEMS are used to clean and treat semiconductor devices, low-voltage switches for radio frequency applications, micro-relay modules, spray nozzles for ink jet printers, and actuators for optical scanners, just to name a few. MEMS devices are becoming widely used in various industries. For example, in the automotive industry MEMS pressure sensors measure engine oil pressure, vacuum pressure, fuel injection pressure, transmission fluid pressure, various line pressures, tire pressure, and stored air bag pressures. MEMS temperature sensors can be used to monitor oil, antifreeze, and air temperatures. Other industries are also finding uses for MEMS devices. For example, in the disc drive industry MEMS devices are being contemplated to use as microactuators to very precisely position magnetic transducers over very closely packed tracks containing data.
MEMS devices are typically fabricated by overlaying a semiconductor wafer made from silicon with layers of oxides, metals and other materials necessary for circuit construction. Patterns are formed on and within these layers in order to make a circuit plan of the device. The patterns usually include elements for two-dimensional and three-dimensional interactions of the MEMS device circuit plan.
The patterns are formed in the MEMS device by a combination of masking and etching. Masking includes fabricating a mask that is in the form of a pattern and then positioning the mask on, or near, the surface of the MEMS device. The mask establishes how the MEMS device is to be etched. It is etching the MEMS device that permanently places the pattern into the MEMS device. Etching is typically done by removing the top layer(s) from the MEMS device in those areas that are either covered or uncovered by the mask depending on the type of etching that is used to remove the layer(s). Etching processes are either wet or dry, and the goal of any etching process is to transfer the desired pattern to the MEMS device.
Semiconductors are another class of devices that are formed using photolithography, masking and etching. It is contemplated that other devices will also be formed using these techniques.
One known masking method is photolithography which involves forming a pattern onto a photomask and then transferring the pattern to a radiation sensitive layer that has been placed on a semiconductor substrate. The radiation sensitive layer is typically called a photoresist layer. The pattern is transferred to the photoresist layer by exposing the photoresist to some form of light. The light extends through the mask to cross-link the photoresist in the form of the pattern. One of the exposed or unexposed portions of the photoresist is then subsequently removed from the substrate. The device is then etched, or not etched, in those areas of the substrate that are covered by the photoresist.
FIG. 2 illustrates a portion of a wafer 52 that is used in fabricating MEMS device 50. FIGS. 3–4 illustrate a similar wafer 13 in a prior art MEMS device 11 after the wafer 13 has been has been masked and then etched to form a pattern in the wafer 13. The square hole 12 (i.e., pattern) extends downward into the surface 16 of the wafer 13 such the pattern is partially defined by sidewalls 18. The etched pattern forms one or more “square” edges 14 between the surface 16 of the wafer 13 and the sidewalls 18 of the square opening 12. When a mating element, such as an actuator in a disc drive, is inserted into the square opening 12, the square edges 14 have a tendency to chip and crack. This chipping and cracking of the edges 14 generates debris that can negatively effect the operation of the MEMS device and other devices where the MEMS device is used.
FIGS. 5–6 illustrate another typical wafer 19 that has been masked and etched to form a square island 20 on the wafer 19. The square island 20 includes sidewalls 28 that extend upward from an exposed surface 25 of the wafer 19. The island 20 includes similar square edges 22 between the original surface 21 of the wafer 19 and the sidewalls 28 of the island 20. These square edges 22 are similarly vulnerable to chipping and cracking when a mating element is engaged with the island 20. These square edges 22 are also susceptible to damage when the island 20 is grasped by a tweezers or some other handling device to maneuver the wafer 19.
Therefore, what is needed is a MEMS device that is configured to permit mating elements, such as actuators used in disc drives, to be inserted into the MEMS device without damaging the MEMS device. What is also needed is a method of fabricating a MEMS device that permits objects to be inserted into or on the MEMS device with minimal chipping and cracking of the MEMS device.